Treating slaked lime and making pigment therefrom



Patented Aug. 28, 1951 UNITED "STATES PATENT OFFICE I TREATING SLAKEDLIME AND.MAKIN G PIGMENT THEREFROM Harold R. Raftcn,.Andover, Massassignor to Rafiold. Process Corporation, a corporation of Massachusetts-No- Drawing; Application June 20, 1950,

Serial No. 169,287

tinuation in part, andSerial No. 603,112] also a continuation in part,of my then copending", but now abandoned, application SerialaNo.562,273, filed November 6, 1944.

The principal object of my invention is the treatment of slaked lime inthe presence or water, particularly in paste or slurry form-whereby. itis substantially improved-for. use, as; a raw material for furthermanufacture.

An important object of my inventionis-the subjection of slakedlimein-thepresence oi; water to a mechanical processing actionin which shock,attrition or compression of said slaked limeeocours, and the-improvedslakedlime so produced. A further object is themanufacture of pigmentcomprising calcium carbonate by the reaction of treated slaked lime andcarbon dioxide,: whereby pigment of substantially improvedgloss-isobtained, e. g. when used as a coating for paper;

A further object is the production of a calcium carbonate which has arelatively high gloss, and which, in certain cases, is capable of beingvery considerably improved in gloss by further-treatment, by conductinga gascontaining carbon dioxide into a slurry of treated sla-ked lime;

A further object is the production of a calcium carbonate which has arelatively high :gloss and which is capable ofbeing improved in glossbyfurther treatment, by projecting or spray ng. a milk of treated slakedlime into an atmosphere containing carbon dioxide. Y

A further object-is the extension of the range of the conditions underwhich calcium carbonate of a gelatinous type may be produced, and, the

tion of treated slaked lime and sodium carbonate,

whereby pigment of substantially improved characteristics is obtained,particularly ofuimproved gloss, e. g. when used as a coating forpapeiz-Claims. (Cl. 23-456) 2 A further object is the production in the causticizing process of pigment comprising calcium carbonate which hasarelatively high gloss, and which, in certain cases, is capable of beingvery considerably improved in gloss .by further treatment.

,-A further object is the production of pigment comprising calcium.carbonate in the causticizing process conducted at a relatively hightemperature, which has substantially asfine a particle sizeas that.previously made by causticizing at a temperature. below substantially C.

Other objects and advantages of my invention will become apparent duringthe course of the following description.

Slaked lime is widely employed in the arts as a raw material.Particularly is it used in the manufacture of calcium compounds employedas pigments, fillers, or-thelike, such as calcium carbonate, fluoride,oxalate, phosphate, silicate, sulphate and sulphite, or compounds ormixtures which contain one or more metallic radicles in additiontocalcium, such for example as aluminum as in the case of satin white,titanium as in th case of extended titanium compounds, and antimony,barium, lead, magnesium, zinc, zirconium, or the like in compounds ormixtures containing; such metallic radicles. As specific examples:.sl'aked lime may be used in the manufacture oi calcium carbonate eitherby treatmentwith carbon dioxide, or by treatment with sodium carbonatein the causticizing reaction wherein calcium carbonate is producedconcomitantly with sodium hydroxide; or slaked lime may be used to makcalcium fluoride with hydrofluoric acid or a, soluble fluoride; orslaked lime may be used to make calcium sulphite by reaction withsulphur dioxide, or. with a soluble sulphite; or slaked lime may be usedto make calcium oxalate, phosphate or sulphate with oxalic acid,phosphoric acid. or sulphuric acid, or with a soluble v oxalate,phosphate or sulphate, respectively; or to make .cal-cium silicate withsodium silicate; or tomake satin. white with alum; and the like. Allthese reactions are well-known in the art.

The improvement which constitutes the present invention comprisessubjecting sla-ked lime in the presence of water to a mechanicalprocessing action in which shock, attrition or compression ofsaid slakedlime occurswhereby the character-- istics of the slaked lime aremarkedly affected, as are the characteristics'of the products made fromsuchtreatedslaked lime.

considered as suitable.

tual trial of the method of the patent, the fine troduction of carbondioxide into a slaked lime slurry between and 50 C., it. is recommendedthat the lime be slaked under conditions of viaorous agitation. Suchagitation may be carried out with a slow moving agitator, for exampleone having flexible steel fingers, or with a high speedagitator.Examples of such high speed agitators commonly used in the art arepropellers and turbo-mixers. In the Statham and Leek Patent No.2,081,112, issued May 18, 1937, which relates to the manufacture ofcalcium carbonate by spraying milk of lime into an atmosphere of carbondioxide gas, it is directed to Whip the milk of lime into a spray ormist, for exposure to carbon dioxide, with a series of vanes orbladescarried on a shaft.

In the Alton Patent No. 1,379,157, issued May 24,1921, relating to themanufacture of calcium carbonate by causticizing sodium carbonate withaslaked lime slurry, it is directed to reduce calcium oxide (containingsome unburned calcium carbonate) to a finely divided and intimatelymixed paste by grinding it in the presence of water (or without water ifdesired) in a tube mill or a pebble mill, or by passage through millstones, producing a milk of lime thereby, and

then treating it with a solution of sodium carbonate. In the Brooks andRafton' Patent No. 2,062,255, issued November 24, 1936-, relating to themanufacture of calcium carbonate by causticizing sodium carbonate below70 C., it is directed to stir the lime thoroughly during slaking;

scribing the manufacture of calcium carbonate by causticizing sodiumcarbonate between and C., it is recommended. to slake the lime in hotwater with vigorous agitation. This procedure is said, by preventingcrystal growth, to produce a fine slaked lime, which promotes thefineness of the resulting calcium carbonate. Alternatively the lime maybe slaked in cold water, afterwards beating the milk of lime vigorouslyfor a considerable time to bring it to the same condition where it wouldhave been, had it been slaked in hot Water. No specific apparatus isrecommended for the vigorous agitation and beating of the slaked limeslurry, but in the examples given, adequate stirring in a usual time of15 minutes is mentioned, so that the equipment ormixer such as iscommonlyused in the art, may be considered as suitable. This is alsoconfirmed by actual trials of the method of the patent, the calciumcarbonate described being obtained when employing such apparatus. In theHaywood patents, No.*1,984,188, -issued December 11, 1934, and No.2,210,405, issued August 6, 1940, relating to the manufacture of calciumsulphite by spraying milk of lime into an atmosphere of sulphur dioxidegas, itis directed to whip the milk of lime into a spray or mist forexposure to the sulphur dioxide with a paddle wheel device which issimilar to. that employed in the Statham and Leek patent referred toabove.

These patents will sufiice to show the prior art practice of treatingslaked lime in the presence ofLwater for subsequent use in themanufacture dinarily employed in the art for giving a vigorous agitationor beating to lime slurries, such as the propeller type agitator orturbo-mixer, may be This is confirmed by accalcium carbonate describedbeing obtained when employing such apparatus.

' 'In the OConnor Patent No. 2,211,908, issued of various kinds ofpigments. The prior art practice may be briefly summarized as thoroughlyslaking the lime to give a slaked lime containing water, and agitatingit thereafter with the help of vigorous stirring such as may befurnished by flexible finger agitators, propeller agitators andturbo-mixers, or grinding the lime with water to an intimate .mixture bypassage through a tube mill, pebble mill or mill stones, or creating aspray of lime milk with a paddle wheel.

My treatment of slaked lime differs sharply from the prior. art practicein that it employs an entirely different order of intensityand/or time,and although it may employ in certain cases one or more pieces ofapparatus mentioned in the prior art as being used with slaked lime, theintensity and/or time of the treatment with which such pieces ofapparatus is employed in my process brings about an entirely differentresult .from that hitherto obtained. In the practice of my process Isubject slaked lime in the presence of water to a mechanical processingaction in which shock, attrition or compression of said slaked limeoccurs, until an increase of not less than 10% is obtained in itssettling test, as hereinafter described. 'For convenience, "mechanicalprocessing action in which shock, attrition or compression occurs willhereafter in this specification be abbreviated as such mechanicalprocessing action. I shall now give examples of such mechanicalprocessing action which, when carried out for 'a'sufflcient length oftime, will bring about the desired change in the settling test of theslaked lime, together with examples of means for producing it.

I may subject slaked lime to a striking action, in slurry form,or'if-desired in paste form, e. g. in a 'Rafton mill- (disclosed in mythen copending application Serial No. 479,373, filed March 16,

hereof for purposes of cross reference), or in slurry or paste form in ahammer mill, or in any other suitable apparatus wherein slaked limeparatus Whichemploy a striking action are equip- :ment employing more orless radial, revolving,

striking arms or vanes, and the so-called squirj rel cage typedisintegrators using concentric rows of pins on one or more revolvingdiscs. I

may also treat slaked lime by attrition, e. g. in slurry form, as byprolonged milling in a ball mi l; pebble mill, tube mill or rod mill, ore. g. in

paste .form, as by: a. prolonged kneading. act-ion in a pug mill;kneader; 'Banbur-y mixer; .orthe like. I may also subject'sla'kedlimeato compressionaor toicompression andattrition; e. g;. in a :stifipaste form, as ina roller mill with;;e qual .may be pressed out, as byfilter pads orv porous drainage surfaces. Or I may treat slakecllime, e.g. in slurry form, by discharging it througha nozzle preferablyat highspeed, and against a target, if desired: (Ordinary spray nozzles, as

.. well. as so-called atomizer nozzles wherein the suction effect of agas. passing over an openend tubeinduces a flowwhich is converted into aI spray, are-not efiective due to the relatively low speed at whichtheslurry passes through-such nozzles.) Or I may subject, slaked lime inthe presence of water to-any other suchmechanical processing actionwhereby the slaked lime. is"- markedly changed in its settlingcharacteristic as described below, and whereby it will produce pigmentsand the like of characteristics markedly different from those producedby slaked lime as treated in prior art. processes. If the equipmentemployed operates in a batch-manner, it is operated for the requiredlength of time; if it operates in a continuous-manner, the slaked limemay be put through once if'that; is sufficient, and

.if not, it maybe cycled through the equipment for the required numberof times or'for the'required length of'time to obtain the. desiredefiect.

- Whereas I-may useanyof theapparatus indicated.above, or any otherequipment which will eiI'ect-the desired change intheslaked lime, my 1experiments to date; have indicated.- that apzparatus employing astriking action appear-to give muchbetter results than;v other types ofequipment. Of such apparatus, I find the Rafton mill and the hammermillparticularly efiective,

' and these are, therefore, the preferred apparatus for mytreatment ofslaked lime. In a Rafton mill it is the teeth of the circular saw-whichis usually employed as therrotor .elementgwhich strike the material; andin aihammer, millitlis the, hammers of the rotor element which strikethe material. ,The'teeth in the oneo'case and the hammersin the-othermaybe term-ed:.the:p.ercussive members of the rotor element, and, as iswell knownysaid "members propelthe' material subjected to them away-fromand out of their path of travel.

The testing procedure which I have so far found most suitable fordifferentiating slaked lime treatedby my process from the slaked limeoriginally used, as well as from slaked lime treated by prior artprocesses, is a settlin procedure. The specific procedure whichI haveused is simple and has proved very satisfactory for my purpose. Itconsists in thoroughly mixing 4.0 grams (dry basis) of slakedlime-whether in dry, crumbly, paste .or slurry form, with a little waterat room temperature, then making up the mixture with further water toexactly 50cc. in a two ounce bottle graduated in 00s., shakingthoroughly, allowing the mixture to settle overnight, i. e. for 16hours, and then reading the volume of the settled material in cc. Thisreading is termed the "settling test, and where here" in-I speak of asettling test,-I mean thereading obtained whenitheeettling is conductedaccording to the procedure which I have just specifically described; Thedifference in settling tests between several samples under examinationindicates the difference between the samples.

While any increase in settling testbetween'an original untreated and atreated slaked lime has, of--course.. some significance;- I: havefound'that a 10%"increase in the settling test of a'treated slaked limeover thatof'the. untreated slaked lime is about the minimumincreasewhich indicates that a change of the type'I desire has occurred,and I prefer treated slaked lime: which exhibits a much larger increase.'"The: prior art treatmentsof slaked'limaas will be shownbelow, resultin no; or substantiallyv no, increase in 5 settling'itest' over thatof'the original slaked lime. and in some-cases a decrease is evenobserve-d. I find that slaked limes which show 'atieast'a 10% .increasein settling. test after treatment,-and' preferably a: greater increase,yield initheprocesses in which they are subsequently usedi productspossessing propertiesgreatly improved in comparison with the propertiesof products made -in,a similar manner, but with untreated slaked -lime,or,-with slaked. lime treated according to. the procedures of the priorart. While I find it highly usefulto employthe changed settling testot atreated slaked lime for purposes-of difierentiation,

it, is not, however, to be understcodthereby that other tests or:characteristics of the. slaked. lime may not-also be changed; and,the.claims. where a certain increase in settling isrecited as thecriterionor the. change effectedl in the slaked lime, it'is z to beunderstood, that while 'such test-of itself may'notlnecessarily' haveany specific usein the employmentof the slakedlime, it is, nevertheless,an adequate. criterion-of the useful change whichlias takenplace. V Q

*In order to illustrate the results obtained my process, I shall presentdata on the settling tests of slaked limes originally employed and aftertreatment. I shall alsopresent data on the settling testsof slaked limesoriginally employed and after subjection to 'prior art-procedures; sothat the differences between fthe-settling of the slaked limes treatedby my processvand those subjected tothe prior art proce'dures will befully demonstrated.

I now give four examples of the practiceofmy invention.

EXAMPLE 1 I slaked. a sample of lime, in water, usine tlije .water nearboiling. I used sufficient waterft'o produce a final .mud-likeconsistency, I which liequired'about 3' parts by. weight of; waterto' '1part byweight ofjlime. withthe particular lime employed. I agitated thelime during the 'slaking, and then, after the slaking was completed';"'Idiluted the slaked limerconveniently to approximately 20% dryconcentration (of slaked lime), and thenzsubjected it to my preferableprocedure of screening it through 'a'iine mesh wire cloth. I used mesh,but any fine mesh may beuused as desired. I- then passed the screened.slak'ed lime slurry through a Rafton mill, :therotating element(circular saw) of which had; a peripheral velocity of approximately 460feet per second. Whereas once through'rthe-xmill gives an appreciableresult, I passed the slaked lime slurry by preference throughthe mill aplurality 'of times, in "the present instance-20 passes. Anynumber mm 1toe!) passes ormore is-suitable', according to the-results desired. 1 i

EXAMPLE 2 I slaked another sample of lime asin Example 1, diluted andscreened it, then concentrated it to a soft paste form about 33% dryconcentration, and passed it through a hammer mill, in the presentinstance by introducing it radially through a port in the side, of thecasing by means of a screw conveyor into the path of the rotatinghammers, although the slaked lime may be otherwise introduced asconvenient. The hammers had a peripheral velocity of approximately 350feet per second, and discharged the treated slaked lime directly throughan opening at the bottom of the mill. .The treated slaked lime may ofcourse be discharged through a screen or grid but I prefer the opendischarge. I used passes, but here, as in the case of the Rafton milltreatment once through the mill gives an appreciable .result, and anynumber of passes from 1 to or more may be used according to the resultsdesired.

mills act proportionately more rapidly than smaller diameter mills, butin a laboratory mill usually from 4 to 16 hours, more or less, is de-'sirable, and in the present instance I used a 12 hour period. In anyevent, the'time' required is very much longer than that necessary formerely reducing it'to a finely divided intimate mixture or the like,'forwhich a period of some 15 minutes in a laboratory mill'is usually sufli-;cient.

EXAMPLE 4 I used a sample of the same slaked lime as in Example 3, andconcentrated it to a thick paste form at about 44% dry concentration. Ithen subjected it to a prolonged treatment in a kneader. Here, as in thecase with a pebble mill,

the time of treatment required depends upon I agitated with extremevigor a sample of lime slaked as in Examples 1-3, using a propeller agi-'tator-revolving at a speed of about-1760 R. P. M., .for a period of 15minutes, the slaked lime being at a soft pasty consistency ofapproximately 32% dry concentration.

PROCEDURE B I agitated with extreme vigor a sample of the sameslakedlime as used in Procedure A, using a turbo-mixer agitator revolving at aspeed in the neighborhood of 1000 R. P. M., for a period of 15' minutes,the slaked lime being at a heavy slurry consistency of approximately 29%dry concentration. I removed a sample for test, and then continued thetreatment for a period of 105 minutes, making a total treatment of 2hours,- or eight times as long as that of the sample removed for testafter 15 minutes.

PROCEDURE C I subjected a sample of lime slaked as in Examples 1-3, inheavy slurry form at a dry concentration of about 30%, to a grindingtreatment in a pebble mill for 15 minutes, which was suflicient toreduce it to a finely divided intimate mixture.

PROCEDURE D I subjected a sample of lime slaked as in Examples 1-3,diluted to a slurry of approximately 11% dry concentration for one hourto a paddle wheel agitator mounted on a horizontal shaft, the tip of thelowermost paddle dipping into a pool of the slaked lime slurry. Theshaft was revolved at about 520 R. P. M., giving the paddle tips aperipheral speed sufiicient to produce a fine spray.

PROCEDURE E I slaked a sample of lime by the method used in the previousexamples and procedures, namely in water near boiling, using sumcientwater to give a final mud-like consistency, in this case 3 parts byweight of water to 1 part by weight of lime, agitating the lime duringslaking, and then screened the slaked lime after dilution. I then slakeda second sample of the same lime in cold water, using 8 parts by weightof water-to 1 part by weight of lime, without agitation, and thenscreened directly this slaked lime, which was in the form of a thinslurry of approximately 14% dry concentration. I then agitated thislatter sample of slaked lime slurry with extreme vigor,

using a propeller agitator revolving at a speed of about 1760 R. P. M.,for a period of 30 minutes.

(Note.-In all the above examples and procedures, the slaked lime wasscreened in every case, even though that step is not specificallymentioned.)

I have determined the settling tests of the samples of slaked limetreated in Examples 1-4 and Procedures A-E, as well as of the originalslaked lime used in all of the examples and procedures. The results aretabulated in Tables Land II below:

Table I.-Treatment according to present invention Per cent infi'easetinse in est Example Material g based o n the settling test of the originalslaked lime Originfil slaked lime used in i8 x. 1 Slaked lime treated inRufton 36 Mill.

Digging] slaked lime used in 18 x. 2 Slaked lime treated in ham- 30 67mer mill.

Original slaked lime used in 20 Exs. 3 and 4. 3 Slaked lime treated bypro- 26 30 longedpebble milling. 4. Slaked lime treated by pro- 23 15longed kneading.

Table II.T1'eatme'nt according to prior art practice Per cent increasein settling test based on the settling test of the original slaked limeProcedure Material cggitng Original slaked lime usedin Procedures A andB.

Slaked lime agitated extremely vigorously with propeller agitator.

Slaked lime agitated extremely vigorously with turbo-mixer agitator.

Same, but agitated for eight times as long.

Original slaked lime used in Procedure 0.

Slaked lime ground to finely divided intimate mixture in pebble mill.

Original slaked lime used in Procedure D.

Slaked' lime whipped to a spray with paddle agitator.

Slaked lime, slaked in hot water, thick.

Original slaked lime used in Procedure E, (same lime used for slaking asin test directly above), slaked in cold water, thin.

Slaked lime agitated extremely vigorously with propeller agitator.

It will be seen from Table I that in every case.

the subjection of slaked lime to such mechanical processingactionaccording to my invention (Ex test of a given slaked lime broughtabout by such mechanical processing action to which I subject it,- givesreliable evidence of very important improvement in the quality of thepigments which are obtained from such treated slaked lime when thetreated slaked lime is subjected to subsequent. pigment formingreactions, whereby pigments, de

tailed examples of which willbe given latenherein, are obtained muchsuperior to those obtained from slaked lime either untreated ortreated'according to the prior art practices. It thus apparent that agreat advance has been-madein the art of treating slakedlime, and thatmy process will produce slaked'lime from which improved pigments canbesimp y and inexpensively manufactured.

Lime may be slaked :with only enough water to give a dry orsubstantially dry product, which is termed hydrated lime. This is aspecial kind of slaked lime which I will discuss in detail later herein.Or lime may be-slakedwith a moderate excess of water to a crumbly formcontaining Water, or with more water to give a thick mud. or with astill larger quantity of waterto give a slurry. The temperature of thewater used may be anywhere from cold to boilingfand th'dlirne 10 may beslaked with or without agitation. The lime is usually slaked atatmospheric pressure, but'superatmospheric pressure may be used, or,indeed, subatmospheric pressure. With most of the limes with which Ihave-had eXperience' the best results areobtaineclby slaking the lime inhot water near the boiling point using enough Water to give aheavy-mud-like consistency to the slaked lime, and employing vigorousagitation; Therefore this is my preferred method 'of slaking and the onewhich is shown in Examples -L t-herein. It has been asserted that; whenthe slaking-is conducted with enough water to give a thick consistency,such as a mud or the like,

and the-slaking is conducted under vigorous agita tion, the cooler theslaking the better the results; but while this is doubtless true withcertain limes, in most cases it would appear that the optimum resultsare obtained by hot slaking. However, I may, if- I desire, use coldwater in slaking-,'in Whichcase a relatively large proportion of waterto the 'limefea'g. some six to "ten parts of Water to one part'of lime,shouldordinarily be employed if it be desired that the final temperatureof the slaked lime should not be boiling or even very hot; and, also ifI desire, I need not employ agitation. Usually, as stated, relativelylow temperature slaking-gives poorer results, but, as indicated above,there are limes which slake well under these conditions. Sucha'situation is ex-' hibited by'the lime used in Procedure E above (TableII), which lime, when slaked in cold water to a thin slurry withoutagitation, gave the same settlingtest as when slaked in hot water to athick mud with agitation.

- In those cases where lime slaked cold without agitation, or even withagitation, to a mud or slurry, do'es'not give as high a settling test asthe same lime slaked hot with agitation to a mud or slurry, asubsequentvigorous agitation of such lime slakedcold without agitation willsometimes convert it to a condition'where it possesses substantially ashigh a settling test as if the lime were slaked hot with agitation andalso if the lime is originally slaked cold but with some original"agitation, the same result may sometimes be obtained-with a lessvigorous subsequent agitation. However, where a limeis slaked cold to amud or slurry, whether or not'the lime is agitated during the slaking,and where it is necessary to agitate it more or less vigorously afterslaking to improve its quality, this cold slaked lime is merely by thissubsequent agitation brought up to approximately the'settling test whichit would have possessed had the lime originally been slaked under thebest conditions, which for such a lime, is usually hot with agitation.My invention, of course, does not relate to such a procedure wherebylime slaked under less favorable conditions is merely improved to thequality which it would have possessed had it been slaked under optimumconditions. Therefore, where I speak of treating slaked lime until anincrease isfefiected in its settling test of not less than a givenpercentage of the original valve of said test, it is to be understoodthat I mean that said original value shall have been determined on theslaked lime in: question when slaked under substantiallythe optimumslaking conditions for that particular lime.

If t h e lime is slaked to a slurry, it may be used in that condition,or co'ncentra'ted before use ifdesired. If the lime is slaked to athickni'ua; it'inay be used in that condition, Cir diluted and used in adiluted condition or it may be reconcentrated, e. g. to a paste form,before use,

The usual reason for the latter procedure is that while it is desirableto slake a lime thick and to use it thick, it may also be desirable toscreen the slaked lime before use, and inasmuch as it is usuallynecessary to dilute the slaked lime to screen it effectively, especiallythrough a fine mesh, an intermediate diluting sometimes is usefulfollowed by a recencentration. I may also, if desired, treat the slakedlime prior to screening as my treatment tends to reduce any gritpresent. The slaked lime may then be screened subsequent to mytreatment, or not, as desired. My preferred method, however, isto screenthe slaked lime in slurry form before treatment as this avoidscontaminating the treated slaked lime with any impurities present in theoriginal slalred lime; and mypre'ferred methods of treatment, in theirentirety, are those shown in Examples 1 and 2 above.

Instead of employing slaked lime in slurry or paste form which is mypreferred practice, I may employ it in somewhat moist form, e. g. in thecrumbly form already referred to. The amount of water required to slakea lime originally to a crumbly form, or to convert a slaked lime whichhas been dried to a crumbly form, will vary with the lime and otherconditions, but the amount of water finally present in such a crumblyproduct will usually run from 30 to 40%, more or less. When using suchlime in crumbly form, I employ, of course, the appropriate equipment atthe proper intensity and/or time of treatment for effecting the desiredchange in the slaked lime, for example, a prolonged treatment in akneader.

My process is not operable with lime slaked with an excess of water,then dried, and used dry. In order to illustrate the inoperability of myprocess with such dry slaked lime, I cite the following tests whereinlime slaked to a thick mud hot with agitation, was diluted to a slurry,screened, concentrated and then dried, and the dried slaked lime, in drycondition, subjected to two types of such mechanical processing action,one by passing it through a hammer mill (the hammers having a peripheralvelocity of approximately 350 feet per second), and the other bysubjecting it to prolonged (8% hour) milling in a pebble mill. Theresults of these tests are given in Table III.

Table 11 1 .--Treatment of lime staked thick, then It will be seen fromTable III that when lime, slaked in thick form and then dried, issubjected dry to such mechancial processing action, the settling test isnot increased, and sometimes is even decreased substantially.

If I desire, I may use hydrated lime, to which I have referredpreviously herein. If hydrated lime is used, it must be used in. thepresence of water, because hydrated lime, when treated dryas is the casewith lime slaked in excess of wadrated lime, in its customary dry form,is subter, dried and then treated dry- -shows substantially no increasein settling. test when subjected to such mechanical processing action.However, when subjected to such mechanical processing action in the wetcondition, it does show a substantial increase. The tests presented inTable IV are illustrative of the effect of subjecting hy drated lime inits customary dry or substantially dry condition to two types of suchmechanical processing action, one by passing it through a hammer mill(the hammers having a peripheral velocity of approximately 350 feet persecond), and the other by subjecting it to aprolonged (8 hour) millingin a pebble mill, as compared with subjecting it when in wet form tosuch mechanical processing action, in this case a prolonged (10 hour)milling in a pebble mill. The lime employed was a good grade ofcommercial hydrated high calcium lime.

Table IV.T.reatment of hydrated lime It will be seen from Table IV thatwhen hyjected to such mechanical processing action, such as treatment ina hammer mill or prolonged pebble milling, the settling test isdecreased;.

whereas-when hydrated lime, in wet form, is subjected to such mechanicalprocessing action, such as prolonged pebble milling, its settling testis substantially increased. Thus I may use hydrated lime, but only, aspreviously indicated, in the presence of water. of producing hydratedlime in its customary dry form, and then adding water before treatment,is considerably greater than the cost of slaking quicklime to a paste orslurry directly precedingtreatment, hydrated lime is not my preferredform of slaked lime.

While I have mentioned my treatment as beingv given the lime afterslaking, it may of coursebegiven during the slaking, preferably beingcontinued thereafter, or it may be given even while pigment is beingmade therefrom, but this is not my preferred procedure, as it is notusually asconvenient nor as efficient as treatment after slaking andbefore pigment is madetherefrom.

The slaked lime I have referred to so far herein is that obtained byslaking ordinary high calcium lime, but my process is equallyapplicableto lime containing magnesia, which has been slaked, such asslaked dolomitic lime, with which, ingeneral, comparable results areobtained. For

example, a sample of dolomitic lime, after being slaked hot withagitation to a thick mud, gave a settling test of 14. This slaked lime,after subjecting it to such mechanical processing action, in this caseto a milling in slurry form for 11 hours in a pebble mill, gave asettling test of 21, an increase of 50% over the settling test 7 of theoriginalslaked lime.

However, as the expense 13 pe ne age e. ean. a k etal DY I Ph S? phate,tetraphosphate, or hexametaphosphate uc as e e nr or the ke. or el meize edium a ts o alky napht ulp'h nie c ds g kil i c a n u h a Bax 1 othe presence of a wetting agent; a large number at whiehfer w l wn in'tha v nd thi u of ad ion gen m y, t m a a en'e firiel ffe ecm p oces s h ain re sin t efi e e iy- In some eas s. owev the pr s nc 9 di ng e nte is lf mar-l wer omewhat he e t in tes at the er e ne slated. ime bu the ujec on o s h m cha ica lireeessine act on then increase it alth ugh.emeeeses not so h h a p int s in the ab. eaee of t e di pe sin a e t. Imayalso treat the slalged lime in the presence of an adhesivewhiohoperate on a slurry 'to. operate more ef-- Any of the abovementioned addition agents isusually employed in an amount ranging froma-small fraction of 1% up to about 5% on the slaked lime, depending uponthe material used and the .efiect desired. However sometimesmore may beused to advantage, e. g. up. to 8% or more of alpha protein (derivedfrom soya beans),

which gives an excellent thinning effect at such.

percentage. Casein derived from milk gives a thinning effect, usingabout 4%. agents are usually added in solution, but may be added inmoist form, or in some cases in dry form if desired. As mentioned above,some addition agents afiect the settling test, so that it is desirableto conduct the settling test inithe absence of addition agents. Insomecases the addition agent may be removed after treating slaked limein the presence thereof, e. g. by washi g, before making thesettlingtest on the treated slaked lime. If this is not feasible, thesettling test may be made on the slaked lime which has been given thedesired treatment inthe absence of. the addition agent; and the additionagent maythen be used during the treatment on the.

basis of the procedure determined in its aha sence. Itshouldbeemphasized that suitable addition agents are useful to produce improvedresults such as indicated, but that they do not alter the essentialnature of the process. These additionagents add expense to the processand any improved result obtained must be balancedag-ainst'the added costin any given case. Fur-e thermore it must be ascertained whether or notthe presence of any given agent will be 816N211?- tageous, or withouteffect, or disa.dvantageo.us, in the use to. which the slaked lime issubsequently to be put, and that, factor must also be. taken n ns deratn- .1 have tried subjecting quicklime, e. g. in DOW- der f .orr'n ,,-to, such mechanical processing action, such grinding in a pebble mill fora period of eight hours, both alone, and in the presence o f a, smallamount of carbon black as a grinding aid or -t-antiacompaeting agent butin neither case was there any increase in the-settling; test Theaddition of thetreated lime after slaking when compared with thesettlingtestof the original lime after be applicable to driicklim; l

I shall now give examples of pigments pro+- slaking. Hence myprocessdoes not appear to duoed by reaction of slakedlime, treateda's derflscribed herein, with a reagent adapted to pro-- duce a carbonate withsaid 'slaked lime, in the first instance with carbon dioxide, and intlie-- second with an alkaline earth carbonate such as sodium carbonate;

Having treated my slaked lime by subjection in the presence of watertoisuch mechanical processing action until an increase is effected inits settling test of not less than 10% of the original value of saidtest, I then subject it"to' carbonation' with carbon dioxide to formcalcium'carbonate if itbe a high calciumlime; ort'oforrn" calciumcarbonate magnesium 'hy droxide or calcium carbonate magnesium basic"carbonate-or the'like if it be a lime containing;-

magnesia such as dolomitic lime; e I

Iii-order to illustrate the results obtained-in my process I presentdata on pigment commie-"'- 1ing calciu'm'carbonate made according to my?process employing'slaked lime which'has been subjected in --;thepresence of water tosuch I also present data on corresponding pigmentsmade according to prior art procedures wherein the slakedlime has notbeensubj'ected to such action, so that the differences between thepigments made by mechanical processing action.

my process an'dthose' made by the prior art processes will be fullydemonstrated. I

As stated previously, while I may use 'anygof the apparatus indicatedfor subjecting sla kedj lime 'to such mechanical processing action, .I-prefer the Rafton mill and the hammer mi l'l" as th y areparticularlyefiective; In order.

prepare the slalzed lime for production of pigment comprising calciumcarbonate upon which data" is presented herein, I treated some slaked"lime in the presence of water in a Rafton mill, and also treated someina hammer mi1l,.a cfor ing to: llus ti e r ce ur and il IPRDCED RE FEhis is the same sample of high calciumlime treat xample 1 above, withthe results;

- PROCEDURE I slaked a sample of dolomitic lime inwater;

I I used suffic'ient water 'to produce a final mud-like consistericy;which required about 2parts of water to 1 part"v using the water nearboiling.

by weight of lim'e'with the particular lime employed. I agitated thelime during the slat-king,

and then, after the slaking was completed, I

diluted the slaked lime, to a proper consistency for screening, about32%, screened it through mesh wire cloth, thenfconcentratedit to'a pasteform about 50% dry concentration, and

passed it through a hammer mill, inthe presentinstance by introducing itradially through aa port in the side of-the casing by means of a screw,-

conveyor into the path of the rotating hammers, although the slaked limemay be otherwise, introduced as. convenient.

18 but. here, as in the case of the Rafton mill treatmerit, once throughthe mill gives an appreciable result, and any number of passes from 1 to20 or more may be used according to the results desired." The slakedlime before treatment in the hammer mill had a settling test of 17, and

after treatment had a settling test of 22, an increaseiidue to treatmentof 29% based on the original test.

I then subjected the slaked lime of Procedures F and G to carbonation ina number of different ways of which the following examples areillustrative. EXAMPLE I subjected the slaked lime treated in ProcedureF, in slurry form, to gas containing carbon dioxide by leading the gasinto the body of the slurry under its surface according to that methodof gas introduction as described in the Rafton and Brooks Patent No.2,058,503, and I employed an apparatus similar to that describedtherein. The concentration of the carbon dioxide in the gas employed wasapproximately 22%, and the concentration of the slaked lime slurrycarbonated was such that. after carbonation was completed,

the slurry contained approximately 13% calcium carbonate by weight. Thetemperature of carbonation was approximately 24 to 27 C. A propelleragitator was used revolving at a speed of 1760B. P. M. which producedvigorous agitation in the carbonating vessel, which was of a verticalcylindrical type.

I then carried out a companion experiment, like Example 5 in everyrespect except that the slakedlime before carbonation, instead of beingsubjected to such mechanical processing action as defined herein, wastreated accordin to the prior art practice by subjecting it to vigorousagitation, as described in Patent No. 2,058,503.

The calcium carbonate produced in Example 5 and in its prior artcompanion experiment were tested as follows: for per cent adhesiverequirement (in this case casein requirement) bythe usual test employedin the art, 1. e. spreading on paper" successivev aqueous calciumcarbonatecasein mixes containing various percentages of casein, until amix was obtained strong to No. 5, but weak to No. 6, Dennison wax; foroil absorption by the usual linseed oil rub-out method; and {or percentgloss by calendering coated sheets (of the proper strength as producedin the above adhesive strength test), giving each sheet two passesthrough anip of a calendar for coated paper and determining the per centgloss on an Ingersoll glarimeter. The physical characteristic as togelatinous or non-gelatinous quality of the calcium carbonate was alsoobserved. The results are given in Table V.

Table V Per cent Calcium Car- Physical charcasein Oil Ab- Per centbonate acteristic requiresorpticn gloss ment Example 5 Gelatinous.. 28'50 70 Companion prior Non-gelatinous" 45 63 56 art.

1 is much superior.

16:5 cium carbonate'has a much higher settling test than thenon-gelatinous.

By the-term gelatinous as used table'and elsewhere herein I mean thatthe pigment comprising calcium carbonate so designated, exhibits a veryslow filtration rate, has a rather soft and unctuous feeling in filtercake form, ex hibits marked shrinking on drying, and dries to a cordingto prior art practice, under conditionsotherwise similar to thecompanion experiment shown above, excepting only as to'concentration ofthe calcium carbonate in the slurry, it was necessary, in order toobtain a gelatinous calcium carbonate, to'use a concentration notsubstantially higher than 5%. As the prior art op eration at-such a lowconcentration greatly reduces the output of equipment and also 'gives'great difficulty whenfiltering or otherwise dewatering dilute slurries,the operation according,- to my present process at a much higherconcen-' tration, such as approximately 13% or even higher, e. g. atabout 15% or thereabout, extending as it does the range of concentrationat which gelatinous calcium carbonate may be produced. Moreover,gelatinous calcium carbonate obtained under the prior art conditions,

although it gives a high gloss, has the disadvan-.

tage that it possesses a slightly yellow tinge and a rather pooropacity. The gelatinous calcium carbonate of Example 5, however, isunexpectedly,

markedly whiter and much more opaque, both, highly desirable qualities,and additionally has in most cases a lower adhesive requirement. Thus bymy present process I have achieved all these. valuable advantages.

EXAMPLE 6 I subjected the slaked lime treated in Procedure F to gascontaining carbon dioxide in the same manner and in the same apparatusas used in Exrather than the approximately 13% of Example 5, and thetemperature of carbonation was ap-' proximately 40 C. instead of theapproximately 24-27 C. of Example 5.

I then carried out a companion experiment,

like Example 6 in every respect'except that the slaked lime beforecarbonation, instead of being subjected to such mechanical processingaction as defined herein, was treatedaccording to the. prior artpractice by subjecting it to vigorous 7 agitation as described in PatentNo. 2,058,503.

These two calcium carbonates, as well as all the other pigmentscomprisin calcium carbonate described in the subsequent examples, wereof a non-gelatinous nature, and thus do not give so high a gloss as theExample 5 calcium carbonate.

The calcium carbonates produced in Example 6 and in its prior artcompanion experiment were 5 tested similarly to the calcium carbonatesof Ex-- ample 5 and its companion experiment, and the results are givenin Table VI.

in the above It is to be noted that Example 6 calcium carbonate of thepresentinvention shows a slightly lower casein requirement, a slightlyhigher oil absorption, and a higher glossthanthe prior art calciumcarbo'natew-The higher gloss; with the other characteristics fairlyclose respectively to one anotherfrepresents a desired improvementinquality. r

Example 6 calcium-carbonate and its companion prior artcalcium carbonatewere then subjected to a treatment to improve the casein 20 requirement,oil absorption and "gloss; in this case the treatment disclosed in myPatent No. 2,451,448, issued October 1-2, 1948, namely" by passing thecalcium carbonates inasterorm through a hammer mill, in the presentinstance are??? I then carried out a companion experiment, as before,like Example 7 in every respect except that the slaked lime, instead ofbeing subjected to such mechanical processing action, was treatedaccording to the priorart practice by subjecting bonates were tested.'Theresultsonthe two calcium carbonates as originally produced, as 'wellas after treatment in the hammer mill, are all given in Table VIII.

Table VIII fPer cent reduc- I I Per cent reducg ga tion in casein h tionin oil P 0 Per 0.9m; Increase ,Calcium Carbonate re mm requirement Sabsorption 3 gloss lgent based on the 0 Ion based on the loss b-ased onthe original as 100% original as 100 ongmal as 100% Example? -Q I 23 4242' Example 7, passed through hammer I mill times 11 52 29 31 Companionprior art 15 3l I. 41 Companion prior art, passed through hammer mill 10times 8 47 23 26 3 empl yin 10 passe sf flests. wer then mad on the sotreated fi lciulmvcarbonates andtheresults 0 are given in Table VII,

It W111 be noted rrom'ramevm that, anhough the casein requirement andoil absorption of Example '7, calcium carbonate are not 'so low as .TqbLe VJI j Per cent reduc- Per cent reduc- P M Cent tion in casein tion inoil P qentmcrease casein requirement on absorption P C m gloss Calcium.Carbonate re based'on the SM based on the m has-e? on the q toriginal-(in p Ion original-(in Gloss ongmal (m P Table "VDas Table W asTable VI) as mill 10 times..' l 10 55 32 35 63 17 Companion prior art,assed through It will be notedby comparison ofr Tab1e.VII with Table VI,that both calcium carbonates are improved by the treatment ,given them.Q0m paring Example-6 calcium carbonate ,with the companion prior artcalcium carbonate it will be seen that its casein requirement isslightly lower, its oil absorption the same, and particularly, that t imrqremen i los scp si erably greater. This shows that not only is Example6 calcium carbonate of the present, invention of better gloss asoriginally produced, but that it is also susceptible to greater.improvement in gloss by subsequent treatment than is the companion priorart calcium carbonate.

I subjected the slaked lime treated ;in Proce- I the correspondingvaluesfor the companion prior art calcium carbonate,the percentagereduction obtained in both oil absorption and casein reduction issomewhat greater in the treated Example 7 calcium carbonate than in thetreatedcom panion prior art "calcium' carbonate, and the values forthese properties for the treated Example calciumcarbonateare withinreasonable 'limits'ef what is commercially desired. But what is chieflynoteworthy is that the calcium carbonate of Example 7, althoughoriginally being only very slightly higher in gloss than the prior artcalcium carbonate, is very substantially "improved in gloss bysubsequent treatment, whereas the companion prior art calcium carbonateis actuaiiysemew'hatj lowered in gloss by subsequent treatmentjThisillustrates that the calcium'carbonate of'the "present inventionproduced under these conditions possesses the val- 'qharaqtfisii f b'"Emilie Susceptible to greater improvement, particularly as to gloss, by

namely they were passed 10 times through' ahammer mil-Land theso-treated' calcium car- This was conducted exactly the same as Ex- 20,7 by means of paddles a line mist or spray of slurry from a shallowpool in a carbonating vessel. The paddles were mounted on a rotatinghorizontal shaft which extended lengthwise of the carbonample '7, exceptthat the temperature of carbona- 5 m vessel the U M the paddles dlppmg twas approximately 9 o C. instead of t p the p00]. of at the paddleslowermost p051- proximately 54-5? C. of Example 7. A comtions n fii a 11me n' P gas Damon experiment was likewise carried out the containingcarbon dioxide 15 described in the same as Example 8 with the exceptionthat, as statham and 2 Patent 2,081,112, and I before, the slaked lime,instead of being subemployed slmllar method and Carl-Donating jected tosuch me hanical processing action was Vessel (absorber) t0 describedtherein, treated according to th prior art practice by subthe exception,of coursethat my Slaked lime had jecting it to vigorous agitation. Thecalcium carbeen previously treated s indicated a o bgnates produced weretested as previously and The concentration of the carbon dlOXldB emthenwere subjected to the same subsequent treatp y d was 100%. b inasmuch ash re Was 1- ment as given the Example '7 calcium carbonate ways, abovethe P of lurry in the carbonatin and its companion prior art calciumcarbonate, vessel, a volume of air into which the carbon being passed 10times through a, hammer mill, dioxide was introduced, theactualconcentration and the so-treated calcium carbonates were of carbondioxide in the gas above the slurry was tested. The results on the twocalcium carbonof course much less than 100%, but its actual conates asoriginally produced as well as after treatcentration could not bereadily determined bement in the hammer mill, are all given in Tablecause of the presence of slaked lime spray. The IX. concentration of theslaked lime slurry carbon- Table IX Percent gfig gg f oilab g gg gfi P Ct Percentincrease Calcium Carbonate 3512 gggfigggg sorption ggg gfi gfi310s? based 021 12118 mm originalasl00% orig-inalas 100 Example 8 27 3448 Example 8, passed through hammer mill 10 times n 59 27 21 50 1cCompanion prior art 18 27 33 Companion prior art, passed through hammermill 10 times 8 66 23 17 34 3 It will be noted from Table IX thatalthough ated was such that, after carbonation was comthe caseinrequirement and oil absorption of pleted, it contained approximately 18%calcium Example 8 calcium carbonate are not so low as ,7 carbonate byweight. The temperature of carthe corresponding values for its companionprior 40 bonation was approximately 53-57 C. The shaft art calciumcarbonate, the percentage reduction carrying the paddles was revolvedsufficiently obtained in both oil absorption and casein rerapidly toproduce a fine mist or spray from the quirement by subsequent treatmentis slightly poolinthe carbonatingvessel. greater in the treated Example8 calcium carbon- I then carried out a companion experiment, ate than inthe treated companion prior art callike Example 9 in every respectexcept that the cium carbonate, and that the values for these slakedlime slurry was not previously subjected, properties for the treatedExample 3 calcium carprior to carbonation, to such mechanical procbonateare reasonably close to the values desired essing action, but was onlysubjected to the prior in commercial practice. It is particularly to beart practice of being whipped by the paddles noted, however, thatExample 8 calcium carboninto a, fine pray during the'carbonation, theate has a substantially gher gloss than its comsame as in Example 9during carbonation and panion prior art calcium carbonate, and is veryas described in Patent No. 2,081,112. m h m re i p v in gloss bysubsequent tre The calcium carbonates produced were tested m than is sCOmDaIIiOII Prior art calcium as previously, and then were subjected tothe carbonate, which again illustrates the marked same subsequent tr att as given in Exam impovement brought about y e Present ple 8, i. e.were passed 10 times-through a ham- Ven mer mill, and the so-treatedcalcium carbonates EXAMPLE 9 were also tested. The results on the twocalcium Isubjected the slaked lime treated in Procedure carbonates asOriginally produced, 215 W ll a F, in slurry form, to gas containingcarbon 11- after treatment in the hammer mill, are given oxide. This wasdone by whipping into the gas in Table Table X gg gg lifiififltf on ttiPer cent Percentigsgmse calcium carbonate requite- {ggg ggggg sorptioniggg ggg fi Gloss based on the ment original as original as 100 originalas 100% Example 9 36 47 45 Example 9, passed through hammer mill 10times 15 51 a1 21 52 1s Companion prior ar 32 44 36 Companion prior art,passed through hammer mill 10 times 14 56 33 25 43 19 2'2 viouslyherein, and werefthensubjected to the same subsequent treatment as givenin. Example 9, i e. were passed 10 times through a hammer mill, and theso-treated pigments were also such mechanical processing action, isreason- 5 tested. The results onthe two pigments as origiably like thecompanion prior art calcium carnally'produced, as well as aftertreatment .in the bonate produced by the process of Patent No.hammermill, are given in Table XI.

Table XI Percentreduc- Per centreduc Per Cent V Per centincrease Calciumcarbonate magnesium basic casein gg g g ig Oil abgigg g Per Cent ingloss carbonate requireg d th sorption b d p h Gloss based on the e e V6 1 original asl00% original as 100% ongmal as 100 Example 10 55 86 60ExamplelO, passed through hammer mill 10 times 21 .62 68 21 74 23Companion priorart 45 80 55 Companion .priorart, passed through hammermill 10 times 20, 56 59 26 67 22 2,081,112 in respect to caseinrequirement and oil absorption; and While the gloss of both calciumcarbonates is improved by subsequent treatment, nevertheless the glossboth before and after treatment is substantially better for Example 9calcium carbonate of the present invention than it is for the companionprior art calcium carbonate.

In this connection it is to be noted that a sample, which I have tested,of calcium carbonate commercially produced by the prior art process ofPatent No. 2,081,112, does not exhibit as'good characteristics, inrespect to improvement in gloss by subsequent treatment, as does theexperimental sample of prior art calcium carbonate made by the processof that patent, and reported in Table X, in that I found that saidcommercial sample was not improved in gloss,

but rather was even slightly decreased in gloss,

by subjection to a hammer mill treatment.

EXAMPLE 10 I subjected the slaked dolomitic lime treated in Procedure G,in slurry form to a gas containing carbon dioxide. The concentration ofthe carbon dioxide in the gas employed was approximately 22%,and-theconcentration of the slaked dolomitic lime slurry carbonated wassuch that, after carbonation was completed, the slurry containedapproximately of the calcium carbonate magnesium basic carbonate byweight. The temperature of carbonation was approximately 60 C. Theapparatus employed was the same as that used in Example .5. Thecarbonation was continued until a sample withdrawn from the mix gavearesidue of ignition of substantially 50-51%. The composition of thepigment produced was the same as that described in Rafton Patent No.2,049,021, issued July 28, 1936, and the method employed was also thesame as in said patent with the exception only that in the presentinstance the slaked dolomitic lime was subjected to such mechanicalprocessing action in paste form before carbonation.

I then carried out a companion experiment like Example 10 in everyrespect except thatthe slaked dolomitic lime, instead of beingsubjected, prior to carbonation,-to such mechanical processing action,was only subjected to the agitation customarily given the slakeddolomitic lime in the prior art as described in Patent No. 2,049,021.

The pigmentsproduced were tested as pre- It is seen from Table XI thatExample 10 pigment made by the general .procedure of Patent No.2,049,021, excepting only for subjecting the slaked dolomitic lime priorto carbonation to such mechanical processing action, is not quite sogood as the companion prior art calcium carbonate magnesium basiccarbonate produced by the process of Patent No. 2,049,021 in respect tocasein requirement and oil absorption, but by subsequent treatmentarrives at approximately the same casein requirement, with a somewhathigher oil absorption. However the gloss, both before and aftertreatment, is better for Example 10 pigment of the present inventionthan it is for the companion prior art pigment, and that is sufiicientlyimportant from a commercial standpoint to constitute a desiredimprovement in the pigment.

In each, pair of the above examples and companion tests, the same supplyof quicklime was used for producing the slaked lime employed therein. Inall the above examples and companion tests the carbonation was carriedout for convenience at substantially atmospheric pressure, but it is tobe understood that the comparative results obtained are, in general,analogous Whether the carbonation be carried out at atmosphericpressure, subatmospheric pressure or superatmospheric pressure.Moreover, for convenience, the concentration of the gas containingcarbon dioxide employed was in most cases approximately 22%, but thismay be varied from down to a fraction of 1% if desired,

with, in general, analogous comparative differences in results. Likewisechanges may be made in the other variables involved, such for example asin the temperature, vigor of agitation, concentration of slurry, rate ofcarbonation employed, and the like, but here again the same relativedifferences are found between the pigment comprising calcium carbonateof the present invention and the comparative pigment of the prior art,taking into consideration, of course, the differences in thecharacteristics and quality which changes in these variables are knownto produce.

I have given as examples pigment comprising calcium carbonate producedby the general procedure of several prior art methods, the methods beingchanged, however, in respect to the fact that the slaked lime .used wassubjected in the presence of water, prior to carbonation, to Suchmechanical processing action until an increase was .efiected in itssettlin test of not less than of the original value of said test. I haveshown in the tables and in the discussion the improvements obtained overthe corresponding prior art pigments. I have used as illustrations ofprior art methods of producing calcium carbonate: (1) that shown inPatent No. 2,058,503, both in the range in which the process of thatpatent produces a gelatinous calcium carbonate and in the range in whichthe non-gelatinous variety is produced; (2) that shown in general inPatent No. 2,058,503, but above the temperature range of that patent;and (3) that shown in Patent No. 2,081,112. It is to be understood,however, that my invention is not limited to the carbonation of slakedlime by such prior art methods, as I may employ any method ofcarbonating slaked lime with carbon dioxide, 3, large number of whichare known. I have likewise used as an illustration of a prior art methodof producing calcium carbonate in association with another compound, e.g. calcium carbonate magnesium basic carbonate, the general procedureshown in Patent No. 2,049,021. The process of that patent produces aspecific type of calcium carbonate magnesium basic carbonate, but inthat patent there is described a number of other processes for producingcalcium carbonate magnesium basic carbonate of somewhat differentcharacters and compositions by the treatment of slaked dolomitic limewith carbon dioxide under other condtions. It is to be understood thatall those so-clescribed calcium carbonate magnesium basic carbonatematerials, as well as others similarly produced, where the slaked limeis'not completely dissolved by the carbon dioxide in the process, aresusceptible of substantial improvement by utilizing the method disclosedherein in connection with their manufacture. For example, in thetreatment of slaked dolomitic lime with carbon dioxide to extract abouttwo thirds of the magnesia present as magnesium bicarbonate, which isseparated as a solution from the residue for subsequent recovery of themagnesia, the residue consists of calcium carbonate magnesium basiccarbonate containing only approximately one third of the magnesiaoriginally present in the dolomitic lime. The residue has been used as apigment, and said process which produces that pigment, when employingthe slaked dolomitic lime after treatment as described herein, producesa pigment of quality substantially improved over that previouslyobtained. Likewise there are many other processes wherein magnesia isseparated in whole or in part from slaked dolomitic lime by variousreagents, and the insoluble residues from such processes, whethercalcium or magnesium com:- pounds, or both, are improved by pretreatmentof the slaked dolomitic lime employed as described herein.

Furthermore, a calcium carbonate magnesium carbonate or basic carbonateproduct may be made by mixing slaked lime slurry, made, if desired, froma high calcium quicklime, with magnesium hydroxide slurry and thencarbonating the combined slurries. In this case, also, the product maybe improved by pretreating the slaked lime in the manner describedherein, and sometimes it is also desirable to pretreat the magnesiumhydroxide, either in paste or slurry form, in the manner describedherein for slaked lime, and mix the two pretreated slurries, prior tocarbonation; or the two slurries may be mixed before treatment, and themixed slurry treated, and then carbonated; or material other thanmagnesium hydroxide may be mixed with slaked lime prior to carbonation,treatment being given as just indicated, and co-precipitated with thecalcium carbonate. Moreover, by carbonating slaked dolomitic lime withcarbon dioxide in quantity sufiicient only to carbonate the calciumhydroxide present, calcium carbonate magnesium hydroxide is produced; orby using somewhat more carbon dioxide a mixture of that compound andcalcium carbonate magnesium basic carbonate is produced; and thosematerials also are procured of an improved quality when the slakeddolomitic lime employed has been previously treated as described herein.

When I produce pigment by subjecting slaked lime to'carbon dioxide, thecarbon dioxide, when it reacts with slaked lime which has been subjectedto such mechanical processing action, may be present either in the formof a gas, in the form of a solution in water, in the form of calciumbicarbonate or magnesium bicarbonate, or in more than one of the aboveforms. In respect to the carbon dioxide being present in the form ofsuch bicarbonates, it is well known that calcium carbonate can be madeby the treatment of a solution of calcium bicarbonate with slaked lime.A common example of the practice of this procedure is in thepurification or softening of hard water where calcium and/or magnesiumbicarbonate with or without additional free carbon dioxide is naturallypresent either alone or with other dissolved materials. When slaked limeis added to such hard water, calcium carbonate is precipitated either inrelatively pure form, or containing other materials according to theoriginal composition of the water, for example sometimes magnesiumhydroxide or magnesium carbonate or basic carbonate, as well asimpurities of iron and the like. Sometimes other reagents such as sodiumcarbonate and/or alum are also added to secure a more completeprecipitation. Also Where the water contains other ingredients inaddition to the calcium bicarbonate, which ingredients, however, areless apt than the calcium to cause difiiculty in the subsequent use ofthe water if they are not removed therefrom, a so-called selectivesoftening is sometimes practiced. Slaked lime (with or without otherreagents such as sodium carbonate and/or alum) is used to remove byprecipitation only the calcium bicarbonate and/or other bicarbonateand/or free carbon dioxide content of the water, either in whole or inpart, or with only minor quantities of the other constituents of thewater; and, after filtration, centrifuging, sedimentation or the like,of the precipitate formed, the remainder of the constituents still insoluble form are-permitted to remain in the water, which maysubsequently be treated by recarbonation, addition of polyphosphates orthe like. This gives a partially purified, not completely softened,water, but nevertheless a water which is satisfactory for many purposes.

The calcium carbonate derived in such manner and from such processes,and removed by any of the methods indicated, whether such calciumcarbonate is substantially pure or contains other ingredients, isimproved in respect to the various qualities, as already indicated ingeneral, when slaked lime treated as described herein is used. However,because of the fact that the calcium in the calcium carbonate may notall be derived from the slaked lime, but partly from the calciumbicarbonate dissolved in the water treated, the

improvements may not insomecases-be so great as those illustrativelydisclosed: herein.

It is nowclearthat any method ofproduc-ing pigment comprising calciumcarbonate by the reaction of carbon dioxide'in any of itsforms, asdescribed above, with slaked lime treated as described hereingives'pigments comprising calcium carbonate of markedly improvedqualities.

I shall now give examples of. pigments produced with slaked lime treatedas described herein, by reaction with analkaline earth. carbonate suchas sodium carbonate.

Having treated my slakedlime by subjection in the presence of waterto.such-mechanical processing action until an increaseis' effected in, itssettling test of not less than of the original value of said test, Ithen react it with sodium carbonate to form calcium carbonate, if itbe-"a high calcium lime, or to form calcium carbonate magnesiumhydroxide if it be -a lime containing magnesia such as dolomiti'c lime.This reaction between lime and sodium carbonate is, of course, known asa causticizing reaction, and usually is carried out in liquid or slurryform in an aqueous medium in any of the apparatus customarily used, suchas in a: tank provided with an agitator, preferably one which producesvigorous agitation, for example a turbo-mixer agitator. The reaction maybecarried out at a relatively high temperature or at a lowertemperature, as is well known in the art. 'It may be carried out in onestage, generally employing asconsiderable excess of sodium carbonate; ormore usually, and preferably, it is carried outiintwo. stages, in thefirst of which a. stoichiometrical excess of lime is used to obtain asodium. hydroxide: liquor of high causticity, and in the second; oiwhicha stoichiometrical excess of sodium carbonate is used in order thatthe calcium hydroxide content of the lime shall be substantiallycompletely converted to calcium carbonate.

When the process is carried out in one stage, there follows aseparation. of the liquor from the pigment, and: then preferably athorough washing of the pigment, after which: it is ready for usedirectly orafter being dried. When the process is carried; out in. twostages, there is a separation of the liquor from the pigment after thefirst stage and. alsoafter the second stage, usually by filtration, thepigment after the second stage being wellwashed to: remove substantiallyall of the associated liquor, whereupon, as before, it is ready for usedirectly, or after being dried.

A screening or other operation. for'separation of grit or oversize iscustomarily practiced. at an appropriate point in the process, e. g: onthe lime after slaking, :and/or prior to'flltration in. the single stageprocess, and/or prior to filtration in the second stage in the two stageprocess. The liquor from the single stage process usually containsconsiderable sodium carbonate which is objectionable for some purposesand the liquor is customarily treated subsequently to remove part or allof this, The liquors from the two stage process which contain sodiumhydroxide with a minor amount of sodium carbonate, may be combined andutilized for any purpose desired.

The causticizing process is also practiced in a continuous manner-,asis'well known in the art, but this procedura'when. practicedv as isusual with continuous settling,;is. in general applicable only torapid'settling. Pigments: comprising cal-- 26- cium carbonate, and isnot generally used where it is desired to produce the finer grades.

To illustrate the results obtained in my process,'I shall present dataon pigments compris- .ing, calcium carbonate made according to the ticeand by my process will be fully demon- 152 strated. Slaked lime toproduce the pigments. according to the prior art was-made by the belowdescribed Procedures H and J, and to produce pigments according to thepresent invention by the below described Procedures I and K. As.

stated previously, while I may use any of the apparatus indicated forsubjecting slaked lime to. such mechanical processing action, I preferthe Rafton Mill and the hammer mill as they are particularly effective;and in Procedures I-and 2.5 K a hammer mill was employed.

A description of Procedures H, I, J and K is now iven.

PROCEDURE H A sample of high calcium lime was slaked in water, using thewater near boiling. Suflicient water was used to produce a mud-likeconsistency, which required about four parts by weight of water to onepart by weight of lime with the particularlime employed, and'the' limewas given thorough agitation both during the slaking and after theslaking was completed, which corresponds to the optimumconditions forproducing slaked lime given in the prior art. This constituted,therefore, a supply of slaked high calcium lime in-;mud-l'-ike formcontaining water, produced by the optimum practice of the prior art, anda portion of this supply was held for use in the manufacture of calciumcarbonate according to prior art methods. The remainder of this supplywas treated for use in the process of my present invention as indicatedin Procedure I below.

PROCEDURE I PROCEDURE J A sample of dolomitic lime was slaked in water,

using the water near boiling. Sufficient water was used to produce amud-like consistency, which required about twoand a quarter parts byweight of water to one part by weight of lime with the particular limeemployed, and the lime was given thorough agitation both during theslaking and after the slaking wasecompleted,v

which corresponds tothe optimum conditions for producing slaked limegiven in the prior art. This constituted, -.therefore, a supply ofslaked dolomitic lime in mud-like form containing waforuse in themanufacture of calcium carbonate magnesium hydroxide according to priorart methods. The remainder of this supply was treated for use in theprocess of my present invention as indicated in Procedure K below.

Paoccnuxr: K

Part of the supply of slaked dolomitic lime produced in Procedure J wassubj cted in mudlike form containing water to the action of a hammermill, having a peripheral velocity of approximately 350 feet per second.As in Pro-'- cedure I, the mud-like slaked lime containing water wasintroduced radially through a port inv the side of the mill casing, bymeans of a screw conveyor, into the path of the rotating hammers, andvwas discharged directly through an opening at the bottom of the mill.The slaked lime was passed through this mill ten times.

High calcium lime of the quality used in Procedure I-l when slaked inthe manner'of Procedure H and then given passes through a ham,- mer millas in Procedure I, is increased in settling test, due to the treatmentof Procedure I, 67% based on the original test of the slaked lime priorto the treatment. Dolomitic lime of the quality used in Procedure J whenslaked in the manner of Procedure J and then given 10 passes through ahammer mill as in Procedure K, is increased in settling test, due to thetreatment of Procedure K, 30% based on the original test of the slakedlime prior to treatment.

The slaked high calcium lime containing water of Procedure H and that ofProcedure I were then each reacted in companion tests with sodiumcarbonate to produce'pigment comprising calcium carbonate, according,respectively, to the methods of the prior art and of the presentinvention. 'Two sets of these companion tests were performed, in onesetthe reaction was conducted at a relatively high temperature, and inofthe present invention. namely Examples l1N,

12N, 13N and MN N standing for New), arranged in companion tests asExamples 11 and MN, 12 and 12N, 13 and 13N, and 14 and MN.

EXAMPLE 11 121.6 grams (dry basis) of the slaked high calcium limecontaining water of Procedure H was diluted with water to 600 cc., andmixed at a temperature of boiling with 450 cc. of an aqueous solutioncontaining 157.5 grams of sodium carbonate. The reaction was carried outat substantially boiling temperature in a vessel under conditions ofvigorous agitation, employing a turbomixer agitator, for a half hour.The mixture was then filtered on a suction funnel, the filter cake waswashed once with 500 cc. of water, and then was made up with water to900 cc. and returned to the original vessel. It was heated to a boilingtemperature, 150 cc. of an aqueous solution containing 26.3 grams ofsodium carbonate was added, and the mixture vigorously agitated asbefore at substantially boiling temperature for a half hour. Themixturewas'screened through a fine mesh sieve, tn'en filtered on asuction funnel, and the calcium carbonate was washed with watersubstantially free from adhering alkali.

The prior art prooes'sused'in Example 11 is that exemplified'bysuch'p'a'tents as Alton No. 1,379,157 and OConnor'No. 2,211,908.

EXAMPLE llN The process of Examplell was followed with the exceptionthat the slaked high calcium lime containing water of Procedure I wassubstituted for the slaked' high calcium lime containing water ofProcedure H.

. EXAMPLE 12 The process of Example ,llwas followed with the exceptionof the temperature. The slaked high calcium lime containing water ofProcedure H and-diluting water-was mixed with the aqueous solution ofsodium carbonate at substantially 25 C., and agitatedat thattemperature. The same apparatus was used as in Example 11, and thefiltrationwas-carried out in the same manner. The second stage of theprocess with additionof thefsecondportion of aqueous solution of sodiumcarbonate was then completed. The prior .art process used in. Example'12 is that exemplified .by such patents as Brooks & Rafton No.2,062,255 and Al len 8;.Lynn No. 2,140,375.

T EXAMPLE 12N I for. the. slahed high. calcium lime Y containing waterof Procedure 190.7 gramsldry'basis") of the slaked dolomitic limecontaining water of Procedure J was diluted with water to 685 cc'., andmixed at atemperature of boiling with 415 cc.'of an aqueous solutioncontaining 162.5 grams of sodium carbonate. The reaction was carried outat substantially boiling temperature in a vessel under conditions ofvigorous agitation, employing a turbo-mixer agitator, for a half hour.The mixture was then filtered on a suction funnel, the filter cake waswashed once with 500 cc. of water, and then was made up with water to900 cc. and returned to the original vessel. It was heated to a boilingtemperature, 200 cc. of an aqueous solution containing 12.5 grams ofsodium carbonate was added, and the mixture vigorously agitated asbefore at substantially boiling temperature for a half hour. The mixturewas screened through a fine mesh sieve, then filtered on a suctionfunnel, and the calcium carbonatemagnesium hydroxide was washed withwater substantially free from adhering alkali.

' EXAMPLE 13N' The process of Example 13 was followed with the exceptionthat the slaked dolomitic lime containing water of Procedure K wassubstituted for the slaked dolomitic lime containing water of ProcedureJ.

EXAMPLE 14 The process of Example 13 was followed with the exception ofthe temperature. The slaked dolomitic lime containing water of ProcedureJ and diluting water was mixed with the aqueous solution of sodiumcarbonate at substantially 25 test of Example 11N is even somewhatbetter than, and the gloss about the same as, Example 12. It is,moreover, to be noted that in comparison with Example 12, the calciumcarbonate of Example 11N is slightly better in oil absorption butsomewhat worse in casein requirement. It is thus apparent that by mypresent process I can produce by causticizing at a relatively hightemperature calcium carbonate (Example 11N) according to the prior art.Specifically it is noted that the settling test is increased, the oilabsorption is decreased, the casein requirement is decreased, and thegloss is increased-all improvements in quality. Particularly notable isthe very great increase in settling test, and the very considerableincrease in the gloss, of the calcium carbonate of the present inventionmade at a relatively high temperature (Example UN) in comparison withthe respective values of the corresponding prior art calcium carbonate(Example 11). Furthermore on comparing Example llN with Example 12,which is the prior art calcium carbonate made at a temperature belowsubstantially 70 0., it is seen that the settling ditions. The prior artprocess used in Example which not only is greatly superior to prior art14 is that exemplified by such patent as Brooks calcium carbonateproduced at that temperature & Rafton No. 2,066,066. (Example 11), butwhich is almost, if not substantially, equal to the much higher qualityprior EXAMI LE MN art calcium carbonate made at a temperature be- Theprocess of Example 14 was followed with 15 ow Su sta t a y C. (Examp ethe exception that the slaked dolomitic lime con- It is noted,furthermore, that the improvement taining water of Procedure K wassubstituted for in the calcium carbonate of my p ocess Over the slakeddolomitic lime containing water of that of the prior art, when made at arelatively Procedure J. high temperature (Example llN over 11), is Thepigments comprising calcium carbonate mu h rea as 130 most of itsproperties than produced in the above examples were then subthe relativeimprovement shown when it is made jected to a series of tests conductedas previously at a temperature below substantially 70 C. (Exdescribedherein. The results of the tests perample 12N over 12). This is to beexpected beformed on the pigments produced in Examples 11 cause, asindicated above, the prior art calcium and 11N, 12 and 12N are given inTable XII, and carbonate when made at below substantially 70 of thoseperformed on the pigmentsproduced in C. (Example 12), is of a qualitymuch higher Examples 13 and 13N, 14 and 14N are given in than that madeat a relatively high temperature Table XIII. The percent increases orpercent de- (Example 11), and thus naturally there does not creasesshown are those of the N examples of the exist the possibility ofefiecting relatively so present invention in comparison with thecorregreat an improvement over the former as over sponding examples ofthe prior art. the latter. However, an examination of the data Table XIIPer cent Per cent Per cent Per cent S increase decrease decrease P t Percent Example s setgllmg minim. ggg; 53 51 2355? 1 0 test tion ment 19 4s29 4o 46 142 42 13 2s 10 62 39 4e 20 e3 12 N 43 10 43 7 15 25 73 16Table XIII Per cent Per cent Per cent v Per cent Y S mcrease decreasedecrease JP It Icr cent Example tes t gg sor t ion l 3 ggi i i .i igzsei n g test tion rnent 13 14 38 2'6- 47 13N 29 107 33 1s 24. s v 55,17'

14 4e 32 '28 es 14 N 44 -4 2s 13 21 25 e9 1 An examination of Table XIIshows the imshows: that the improvement of the calcium car provement inthe calcium carbonates made acbonateof the present invention over theprior cording to Examples UN and 12N, in which my art, when made at atemperature below substaninvention was practiced, over the correspondingtially C. (Example 12N over 12), is, nevercalcium carbonates made inExamples 11 and 12, 0 theless, substantial, and particularly useful isthe increase in gloss shown.

An examination of Table XIII shows, in general, an improvement of thepigments of the present invention (Examples 13N and MN) over thecorresponding pigments of the prior art (Examples 13 and 14) similartothat shown in Table XII, except that here the relative improvement, incertain qualities at least, particularly in gloss, seems to be somewhatless. This relatively lesser improvement is, however, to be'expected ashere the calcim'n carbonate is not but only about 63%, of the totalpigment comprising calcium carbonate, the remainder in this instancebeing magnesium hydroxide. But even as to gloss, a worth whileimprovement is obtained,

particularly in Example 13N of the present invent-ion over Example 13 ofthe prior art (both made at a relatively high temperature). In general,Example 13N is substantially improved over Example 13, and while it doesnot so nearly approach in quality Example 14 (prior art made belowsubstantially 70 0.), as Example llN approaches Example 12, neverthelessit represents a substantial improvement, and pigment comprising calciumcarbonate (calcium carbonate magnesium hydroxide) of this quality(Example 13N) is not obtainable by the prior art method at the sametemperature (Example 13). In the comparison of Example 14N with Example14 (both made at below substantially 70 0.), here again, as in thecorresponding situation in Table XII, it is seen that there is not somuch difference as there is between Example 13N andExample 13, but it issubstantial as to some of the properties and represents a distinctimprovement. As to the slight decrease in settling test noted in Example14N over Example 14, it can be stated that this difference is of littleconsequence because the two settling tests are already so near themaximum test of 50 that the pigments of both Examples MN and 14 would beconsidered of excellent grade as to that particular quality.

In short, then, it is clear that the data presented in Tables XII andXIII demonstrate conclusively the substantial improvement in quality ofpigment comprising calcium carbonate made by the present invention overthat of the prior art, both when the causticizing reaction is carriedout at a relatively high temperature as well as at a temperature belowsubstantially 70 C.; that the improvement appears to be somewhat greaterwith the use of high calcium than with the use of dolomitic lime; thatwith both limes the improvement seems to be relatively greater when thecausticization is carried out at relatively high temperature than whencarried out at a temperature below substantially 70 C. that by thepresent invention there can be produced pigment comprising calciumcarbonate of improved characteristics, notably as to gloss; and that forthe first time, so far as is known, it is now possible to produce in thecausticizing process when conducted at a relatively high temperature acalcium carbonate which has a settling test substantially as high as thecalcium carbonate which hitherto was producible only when thecausticizing reaction was carried out at a temperature belowsubstantially 70 C. As will be readily understood, all this constitutesan important advance in the art.

It is to be understood that the procedures and examples given herein arefor purposes of illustration only, and are not, of course, to beconsidered as limiting.

As has been pointed out, the causticizing reaction, whether conducted ata relatively high temperature or below substantially 70 C., may becarried out as a one stage or as a two stage process. While the disposalof the concomitantly produced liquor containing sodium hydroxidepresents different problems in the one stage and the two stageprocesses, the characteristics of the pigment comprising calciumcarbonate produced are substantially the same whichever process beemployed.

As is indicated in some of the prior art cited, when carrying out thecausticizing reaction at below substanially 70 0., whether in the singlestage process or in the first stage of the two stage process, theimportant point is that the temperature should be maintained at belowsubstantially 70 C. for an original period during which the slaked limeand sodium carbonate are reacted. This may vary from about a few minutesup to an hour or more, depending among other things upon the vigor ofagitation and the concentration of the mix, but once this period haspassed, the mix may then be raised to a relatively high temperature, e.g. to boiling, without substantial effect on the character of thepigment compris ing calcium carbonate which is produced. As will beapparent, this subsequent raising of temperature has, however, one verypractical advantage among others, namely it permits very much fasterfiltration. Moreover, the second stage of the two stage process may becarried out either: (1) at a temperature below substantially 70 0., or(2) at this temperature followed by a relatively high temperature, 'or(3) originally at a relatively high temperature; without substantialefiect on the character of the pigment comprising calcium carbonate.Here again procedures (2) or (3) provide the practical advantage, amongothers, of faster filtration and washing of the pigment.

The several procedures outlined in the paragraph above may, therefore,be considered substantial equivalents insofar as the character of thepigment comprising calcium carbonate produced is concerned, but certainof them, as indicated, offer practical operating advantages.

Instead of using sodium carbonate for reaction with my treated slakedlime, I may use other soluble carbonates, for example the carbonates ofthe alkali metals, potassium and lithium, as well as the rarer caesiumand rubidium, and these all are to be considered the substantialequivalents of sodium carbonate for the purposes of the presentinvention.

In my Patent No. 2,189,832, issued February 13, 1940, page 1, column 2,line 16, through page 3, column 2, line 6, there is described a methodof causticizing which employs sodium bicarbonate directly, or sodiumcarbonate in combination with carbon dioxide. When I speak ofcausticizing herein, I intend to include such variations of thecausticizing reaction as mentioned in the above referred to section ofsaid patent; and where in the claims I use the term soluble carbonate orsodium carbonate, I intend to include therein soluble bicarbonate andsodium bicarbonate, respectively. Where the word soluble is used, it isintended, of course, to mean soluble in water.

Where I speak herein of a relatively high temperature, I mean atemperature above substantially 70 C.

The pigment comprising calcium carbonate of the present invention madeby the causticizing process may after production be treated to improveits casein requirement, its oil absorption, its gloss and the like, byone or more of the various processes referred to herein for thetreatment of pigment. I find that the pigment comprising calciumcarbonate of the present invention made by the causticizing process is,in many cases, more susceptible to improvement by such a treatment thanis the corresponding prior art pigment, and, in any event, the valuesfinally reached for a number of properties in the pigment comprisingcalcium carbonate of the present invention after treatment indicate apigment of better quality than the corresponding prior art pigmentsimilarly treated, the pigment of the present invention in most caseshaving a lower casein requirement, -a-lower oil absorption, andparticularly a higher gloss.

Where I mention improvement-in glossobtained-in my process for thepurpose of differentiating the pigment comprising calcium carbonate ofthe-present invention from the prior art "pigment, it is not, however,to be understood 'therebythat other tests or characteristics of saidpigment-maynot'also be changed; and although such-improvement has use inrespect tothe employmen-t-of said pigment in coated paper, it may notnecessarily haveany specific use the employment of said-pigment forother purposes,

- but it is nevertheless,an adequate criterion of the useful changewhich has taken place insaid piginent'whereby said pigment is improvedfor pur- 'arabic, karaya, tragacanth and the like. I may also usecoating agents, e. g. certain oils, which have proved effectiveparticularly in preventing agglomeration of the calcium carbonateproduced, when dried, such as cocoanut oil, lard oil, rosinoihpalm oil,sperm oil, soya bean oil, olive -oil,-various kinds of fish oils,'aswell as hydrogenated oils and fats, the latter usually requiringsomewhat higher temperatures to maintain them in liquid form. However,assuch coating agents are attacked by the sodium hydroxide formed in thesubsequent causticizing reaction when thecalcium carbonate is so formed,if. I employ them for calcium carbonate made by the causticizingreaction, I prefer to add them later after removal of the sodiumhydroxide.

If Iuse an addition agent, I may, if desired, remove it after the slakedlime has been. treated and before reacting the slaked lime .to form thecarbonate, .e. g., if the addition agent be one which is soluble inwater, I maywash it out of the treated slaked lime, or I may leav theaddition agent with the slaked lime during the :reaction, and, ifdesired, add more of the same, or other addition agent, thereto. Afterthe reaction, the addition agent may be allowed to remain with thecalcium carbonate or may be removed as ,de-'

sired. Furthermore, when the slaked lime is treated in my process in theabsence of an addition agent, I may, if desired, add an addition agentsuch as indicated herein, e. g. in the amounts indicated herein, afterthe treatment of the slaked lime, and either before or during thereaction to form the carbonate, so that the reaction may take place inwhole or in part in the presence of the addition agent; or in certaincases it may be added after the reaction. After the reaction, theaddition agent if previously added, may be allowed to remain with thecalcium carbonate or may be removed in whole or in part as desired.Among the addition agents which may be used in the reaction, Ihave foundcalgon to be particularly desirable, as, among other things, it appears,in certain cases, to reduce the casein requirement of the calciumcarbonate produced besides imparting other beneficial qualities; andalso the coating agents are very useful, particularly if the calciumcarbonate is to be dried before use. Of course, in certain cases, theaddition agent added may reactin whole or in part with the .slaked limeand/orcalciumcarbonate, and in such case it may not be removable.

doned and replaced by application -;S.erial-.No.

. p ior art pi m nt ee.

718,649, filed Dec. 27,1946, which issued as Patent 'No. 2,447,532 ..ofAugust 24, 1948), 453,469, filed August 3, 1942, (now. abandoned and re-April 11, 1947, which issued (as Patent .No. 2,451,448 of October 12,1948), vand455,367,.1iled August 19, 1942, (now abandonedand replaced"by application Serial No. 706,907,.1filed October 31, .1946, .1 whichissued as Patent 2,498,005 of February 21, 1950) to treat pigments madefrom .slaked lime, by compression .or compressionand attrition, bypassing through a nozzle and against .atarget if desired, and;by striklng; 2 1- 191 .O her pigment treatments suehas. prcloneed-iha mil inkneading and thewlilse ha e e se .been

proposed. However. so .fa n en prior ,to' my invention. has ever t ea e-.l-19 a manner, in the presence efwater. the e a lime to b use pi menmeiiui'a tiirean this sharplydist iisuish m inve ti n emth l I .,srr9=esses- Where. .I .siiea ef. a bel ty mean t includ a aratus. em lqxineumb in a trition elements, for example ball mills, pebble m llsre m l antu emilla Where in th c aims s eak 9f Un v-Withou qualification as tocomposition, I mean to include not only high calcium lime, but also limecontaining magnesia, suchas dolomitic lime.

Where in the claims. the processing of. slaked lime is said to takeplace "finthepresence of liquid water, the word liquid .r iers only tothe state of the water.

My eope d neep cet on seriel No.- 170,48

fi e n 2 the disc su o =-Wh1eh is made a part hereof, and to which crossrerer- ,ence is hereby made, comprises subject matter disclosed but notclaimed herein, to wh ch hlaims are presented therein.

While I have describedin detail-the preferred em di n s of m i ve t n.it 15. be un er- :stood that the details of procedure, the types o apparus h rt n o i g ed ents an th arrangement of steps may bewidely variedwithout depa ting item he it-,o my i en i n 0 the scope of the subjoinedclaims.

I claim:

l. I n-a method for the manufacture-0f pig- .ment, the improvement whichcomprises .sub-

. lecting .siaked lime for use inthe manufacture of said pigment, in thepresence of liquid water, said liquid water being present inan amountnot less than 30% .on the combined weight of the'slalred lime and theliquid water, to the percussive action of percussive members of a rotorelement, said members haying .aperipher'al. .velocity of not less than30 feet per. ec.ond, said s a d. lime being p ope led y idgp ci ssivemembers away from and out of thepath of travel of. said percussivemembers, until. bysald percussive action, the settled. yolilme, measuredin cubic centimeters, ,of a suspension of said .slaked in 4.0 gramsv(dry basis) of the slaked lime is a made up withwater to exactly 50cubic centimeters in a Zounce. bottle. graduated in cubic .centimeters,shaken thoroughly and allowed to stand for 16 hours, is increased notless than of the original. value of said test, said standardizedsettling test being conducted upon a suspension. prepared solely fromslaked lime and water,

said original value having been determined upon I the slaked lime .inquestion slaked under conditions of temperature, agitation andproportion of r lime to water, which, for that particular lime, producea slaked lime with the greatest wet bulk.

2. A method according to claim 1 in which the settled volume in saidsettling test is increased not less than 25 of the original value ofsaid test. 3. A methodaccording to claim 1 in which the settled volumein said settling test is increased not less than 50% of the originalvalue of said t test.

4. A method according to claim 1 in which said slaked lime is a slakedhigh calcium lime. 5. A method according to claim 1 in which saidslaked-lime is a slaked dolomitic lime.

6. A method according to claim 1, in which said slaked lime in thepresence ofliquid water is subjected to the-percussive action in pasteform.

7. A method according to claim 1, in which said slaked lime inthepresence of liquid water is subjected to the percussive action in slurryiorm.

8. A method according to claim 1 in which the percussive members of therotor element have a peripheral velocityof not less than 100 feet per 9.A method according to claim 1 in which the percussive members of therotor element have a peripheral velocity of not-less than 200 feet persecond.

10. A method according to claim 1 in which the percussive-members arehammers.

"11. A method according to claim 1 in which the percussive members areteeth.

12. In a method for the manufacture of pi combined weight of the slakedlime and the liquid water, to the percussive action of percussivemembers of a rotor element, said members having a peripheral velocity ofnot less than 30 feet per second, said slaked lime being propelledbysaid percussive members away from and out of the path of travel of saidpercussive members, until, by said percussive action, the settledvolume, measured in cubic centimeters, of a susfpension of said slakedlime after substantially complete settling of the slaked lime in astandardized settling test, wherein 4.0 grams (dry basis) of the slakedlime is made up with water to exactly 50 cubic centimeters in a 2 ouncebottle graduated in cubic centimeters, shaken thoroughly and allowed tostand for 16 hours, increased not less than 10% of the original value ofsaid test, said standardized settling test being conducted upon asuspension prepared solely from slaked lime and water, said originalvalue having been determined upon the slaked lime in question slakedunder conditions of temperature, agitation and proportion of lime towater, which, for

"that particular lime, produce a slaked lime'with the greatest wet bulk,and then reacting said slaked lime, which has been subjected 'to saidpercussive action, in the presence of water with a reagent adapted toproduce a carbonate with said slaked lime, to form said pigment, saidpigment, in comparison with the corresponding .pig-

7 ment produced when said slaked lime is similarly reacted butwithoutsubjecting it initially to said percussive action, being of animproved quality in respect to at least one of the properties ofsettling test, oil absorption, casein requirement and gloss-impartingquality. v 4

3. In a method for the manufacture of pigment comprising calciumcarbonate, the improvement which comprises subjectingslaked lime for usein the manufacture of said pigment, in the presence of liquid water,said liquid water being present in an amount not less than 30% on thecombined weight oi the slaked lime and the liquid water, to thepercussive action of percussive members of a rotor element, saidelements having a peripheral velocity of not less than 30 feet persecond, said slaked lime being propelled by said percussive members awayfrom and out or the path of travel of said percussive members, until, bysaid percussive action, the settled volume, measured in cubiccentimeters, of a suspension of said slaked lime after a substantiallycomplete settling of the slaked lime in a standardized setling test,wherein 4.0 grams (dry basis) of the slaked lime is made up with waterto exactly 50 cubic, centimeters in a 2 ounce bottle graduated in cubiccentimeters, shaken thoroughlyand allowed to stand for 16 hours, isincreased not less than 10% of the original value of said test, saidstandardizedsettling test being conducted upon a suspension preparedsolely from slaked lime and water, said originalevalue having beendetermined upon the slaked lime in question slaked under conditions oftemperature, agitation and proportion of lime to water, which, for thatparticular lime, produce a slaked lime with the greatest wet bulk, andthenreacting said slaked lime, which has been subjected to saidpercussive action, in the presence of an amount of water, insuihcient todissolve the calcium hydroxide content of said slaked lime, with carbondioxide to form said pigment, said pig-ment, in comparison with thecorresponding pigment produced when said slaked lime is similarlyreacted but without subjecting it initially to said percussive action,being of an improved quality in respect to at least one of theproperties of settling test, oil absorption, casein requirement andgloss-imparting quality.

14. A method according to claim 13, in which said slaked lime isreacted, in the presence of water, with the carbon dioxide by leadinggas containing said carbon dioxide into the body of the slurrycomprising said slaked lime and water, under the surface of said slurry.

5. A method according to claim 13, in which the pigment is calciumcarbonate, the slaked lime is slaked high calcium lime, and in whichsaid slaked high calcium lime is reacted, in the presence of water, withthe carbon dioxide by leading gas containing said carbon dioxide intothe body of the slurry comprising said slaked high calcium lime andwater, under the surface of said slurry, while maintaining said slurryat a temperature below substantially 50 0., the concentration of saidslurry being such as to contain not over substantially 15% by weight ofcalcium carbonate when the reaction has been completed.

16. A method according to claim 13, in which the pigment is calciumcarbonate, the slaked lime is slaked high calcium lime, and in whichsaid slaked high calcium lime is reacted, in the presence of water, withthe carbon dioxide by bringing gas containing said carbon dioxide intocontact with the slurry comprising said slaked high calcium lime andwater when said slurry is in the form of a spray.

17. In a method for the manufacture of pigment comprising calciumcarbonate, the improvement which comprises subjecting slaked lime foruse in the manufacture of said pigment, in the presence of liquid water,said liquid water being present in an amount not less than 30% on thecombined weight of the slaked lime and the liquid Water, to thepercussive action of percussive members of a rotor element, said membershaving a peripheral velocity of not less than 30 feet per second, said'slaked lime being propelled by said percussive members away from andout of the path of travel of said percussive members, until, by saidpercussive action, the settled volume, measured in cubic centimeters, ofa suspension of said slaked lime after substantially complete settlingof the slaked lime in a standardized settling test, wherein 4.0 grams(dry basis) of the slaked lime is made up with water to exactly 50 cubiccentimeters in a 2 ounce bottle graduated in cubic centimeters, shakenthoroughly and allowed to stand for 16 hours, is increased not less thanof the original value of said test, said standardized settling testbeing conducted upon a suspension prepared solely from slaked lime andwater, said original value having been determined upon the slaked limein question slaked under conditions of temperature, agitation andproportion of lime to water, which, for that particular lime, produce aslaked lime with the greatest wet bulk, and then reacting said slakedlime, which has been subjected to said percussive action, in thepresence of water with a soluble carbonate to form said pigment, saidpigment, in comparison with the correspondingpigment produced when saidslaked lime is similarly reacted but without subjecting it initially tosaid percussive action, being of an improved quality in respect to atleast one of the properties of settling test, oil absorption, caseinrequirement and gloss-imparting quality.

38 18. A method according to claim 1'7, in which the soluble carbonateis sodium carbonate, and in which the slaked lime is reacted with saidsodium carbonate at a temperature above C.

19. A method according to claim 17, in which the soluble carbonate issodium carbonate, and in which the slaked lime is reacted with saidsodium carbonate at a temperature below 70 C.

20. A method according to claim 17, in which the pigment is calciumcarbonate magnesium hydroxide and the slaked lime is slaked dolomiticlime.

HAROLD R. RAF-TON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 955,814 Leet Apr. 19, 19101,266,339 Statham May 14, 1918 1,372,193 Roon Mar. 22, 1921 1,410,087Welch Mar. 21, 1922 1,552,024 Alton Sept. 1, 1925 1,583,759 Mathers May4, 1926 1,634,424 Hunter July 5, 1927 1,664,598 Dittlinger Apr. 3, 19281,780,821 Henderson Nov. 4, 1930 2,033,954 Rafton Mar. 17, 19362,049,021 Rafton July 28, 1936 2,058,503 Rafton et a1 Oct. 27, 19362,052,255 Brooks et a1 Nov. 24, 1936 2,066,066 Brooks et al Dec. 29,1936 2,068,039 Rafton Jan. 19, 1937 2,081,112 Statham et a1 May 18, 19372,140,375 Allen et a1 Dec. 13, 1938 2,141,458 Bates Dec. 27, 19382,149,269 Brooks Mar. 7, 1939 2,163,385 Sullivan June 20, 1939 2,188,663McClure et a1 Jan. 30, 1940 2,196,949 Young Apr. 9, 1940 2,211,908OConnor Aug. 20, 1940 2,447,532 Rafton Aug. 23, 1948 2,451,448 RaftonOct. 12, 1948 OTHER REFERENCES Lime and Magnesia, by Knibbs, D. VanNostrand 00., N. Y., 1924, pages 51-53,

1. IN A METHOD FOR THE MANUFACTURE OF PIGMENT, THE IMPROVEMENT WHICHCOMPRISES SUBJECTING SLAKED LIME FOR USE IN THE MANUFACTURE OF SAIDPIGMENT, IN THE PRESENCE OF LIQUID WATER, SAID LIQUID WATER BEINGPRESENT IN AN AMOUNT NOT LESS THAN 30% ON THE COMBINED WEIGHT OF THESLAKED LIME AND THE LIQUID WATER, TO THE PERCUSSIVE ACTION OF PERCUSSIVEMEMBERS OF A ROTOR ELEMENT, SAID MEMBERS HAVING A PERIPHERAL VELOCITY OFNOT LESS THAN 30 FEET PER SECOND, SAID SLAKED LIME BEING PROPELLED BYSAID PERCUSSIVE MEMBERS AWAY FROM AND OUT OF THE PATH OF TRAVEL OF SAIDPERCUSSIVE MEMBERS, UNTIL, BY SAID PERCUSSIVE ACTION, THE SETTLEDVOLUME, MEASURED IN CUBIC CENTIMETERS, OF A SUSPENSION OF SAID SLAKEDLIME AFTER SUBSTANTIALLY COMPLETE SETTLING OF THE SLAKED LIME IN ASTANDARDIZED SETTLING TEST, WHEREIN 4.0 GRAMS (DRY BASIS) OF THE SLAKEDLIME IS MADE UP WITH WATER TO EXACTLY 50 CUBIC CENTIMETERS IN A 2 OUNCEBOTTLE GRADUATED IN CUBIC CENTIMETERS, SHAKEN THOROUGHLY AND ALLOWED TOSTAND FOR 16 HOURS, IS INCREASED NOT LESS THAN 10% OF THE ORIGINAL VALUEOF SAID TEST, SAID STANDARDIZED SETTLING TEST BEING CONDUCTED UPON ASUSPENSION PREPARED SOLELY FROM SLAKED LIME SAID WATER, SAID ORIGINALVALUE HAVING BEEN DETERMINED UPON THE SLAKED LIME IN QUESTION SLAKEDUNDER CONDITIONS OF TEMPERATURE, AGITATION AND PROPORTION OF LIME TOWATER, WHICH, FOR THE PARTICULAR LIME, PRODUCE A SLAKED LIME WITH THEGREATEST WET BULK.
 12. IN A METHOD FOR THE MANUFACTURE OF PIGMENTCOMPRISING CALCIUM CARBONATE, THE IMPROVEMENT WHICH COMPRISES SUBJECTINGSLAKED LIME FOR USE IN THE MANUFACTURE OF SAID PIGMENT, IN THE PRESENCEOF LIQUID WATER, SAID LIQUID WATER BEING PRESENT IN AN AMOUNT NOT LESSTHAN 30% ON THE COMBINED WEIGHT OF THE SLAKED LIME AND THE LIQUID WATER,TO THE PERCUSSIVE ACTION OF PERCUSSIVE MEMBERS OF A ROTOR ELEMENT, SAIDMEMBERS HAVING A PERIPHERAL VELOCITY OF NOT LESS THAN 30 FEET PERSECOND, SAID SLAKED LIME BEING PROPELLED BY SAID PERCUSSIVE MEMBERS AWAYFROM AND OUT OF THE PATH OF TRAVEL OF SAID PERCUSSIVE MEMBERS, UNTIL, BYSAID PERCUSSIVE ACTION, THE SETTLED VOLUME, MEASURED IN CUBICCENTIMETERS, OF A SUSPENSION OF SAID SLAKED LIME AFTER SUBSTANTIALLYCOMPLETE SETTLING OF THE SLAKED LIME IN A STANDARDIZED SETTLING TEST,WHEREIN 4.0 GRAMS (DRY BASIS) OF THE SLAKED LIME IS MADE UP WITH WATERTO EXACTLY 50 CUBIC CENTIMETERS IN A 2 OUNCE BOTTLE GRADUATED IN CUBICCENTIMETERS, SHAKEN THOROUGHLY AND ALLOWED TO STAND FOR 16 HOURS, ISINCREASED NOT LESS THAN 10% OF THE ORIGINAL VALUE OF SAID TEST, SAIDSTANDARIZED SETTLING TEST BEING CONDUCTED UPON A SUSPENSION PREPAREDSOLELY FROM SLAKED LIME AND WATER, SAID ORIGINAL VALUE HAVING BEENDETERMINED UPON THE SLAKED LIME IN QUESTION SLAKE UNDER CONDITIONS OFTEMPERATURE, AGITATION AND PROPORTION OF LIME TO WATER, WHICH, FOR THATPARTICULAR LIME, PRODUCE A SLAKED LIME WITH THE GREATEST WET BULK, ANDTHEN REACTING SAID SLAKED LIME, WHICH HAS BEEN SUBJECTED TO SAIDPERCUSSIVE ACTION, IN THE PRESENCE OF WATER WITH A REAGENT ADAPTED TOPRODUCE A CARBONATE WITH SAID SLAKED LIME, TO FORM SAID PIGMENT, SAIDPIGMENT, IN COMPARISON WITH THE CORRESPONDING PIGMENT PRODUCED WHEN SAIDSLAKED LIME IS SIMILARLY REACTED BUT WITHOUT SUBJECTING IT INITIALLY TOSAID PERCUSSIVE ACTION, BEING OF AN IMPROVED QUALITY IN RESPECT TO ATLEAST ONE OF THE PROPERTIES OF SETTLING TEST, OIL ABSORPTION, CASEINREQUIREMENT AND GLOSS-IMPARTING QUALITY.